LARPing, which stands for Live-Action Role-Playing, means exactly that, Live-Action Role-Playing. LARPS differ in many ways but usually they consist of hanging out in a "pub" or "tavern", or just swinging fake weapons at each other all day.

Larping (or LARPing) is short for "Live Action Role-Playing". A live action role-playing game is a form of role-playing game where the participants physically act out their characters' actions. The players pursue their characters' goals within a fictional setting represented by the real world, while interacting with one another in character. The outcome of player actions may be mediated by game rules, or determined by consensus between players.

The first LARPs were run in the late 1970s, inspired by role-playing games and genre fiction. The activity gained international popularity during the 1980s, and has diversified into wide variety of styles. Play may be very game-like, or may be more concerned with dramatic or artistic expression. The fictional genres used vary greatly, from realistic modern or historical settings to fantastic or futuristic eras. Production values are sometimes minimal, but can involve elaborate venues and costumes. LARPs range in size from small private events lasting a few hours to huge public events with thousands of players lasting for several days.

"I got a ton of exercise last weekend larping. It sure is more fun than sitting around playing videogames all day."

It is a game usually played in the forest where you use weapons made out of foam and PVC.
In LARP you usually go back to the dark ages and you give yourself and others a role on the battle field.
That is in short what LARPing is and what it stands for.

What did you do today?
I went LARPing with my class!
Ah, so did you have fun?
Yeah loads of it!

LARPing is short for "Live Action Role-Playing". A live action role-playing game is a form of role-playing game where the participants physically act out their characters' actions. The players pursue their characters' goals within a fictional setting represented by the real world, while interacting with one another in character. The outcome of player actions may be mediated by game rules, or determined by consensus between players.

The first LARPs were run in the late 1970s, inspired by role-playing games and genre fiction. The activity gained international popularity during the 1980s, and has diversified into wide variety of styles. Play may be very game-like, or may be more concerned with dramatic or artistic expression. The fictional genres used vary greatly, from realistic modern or historical settings to fantastic or futuristic eras. Production values are sometimes minimal, but can involve elaborate venues and costumes. LARPs range in size from small private events lasting a few hours to huge public events with thousands of players lasting for several days.

"I got a ton of exercise last weekend larping. It sure is more fun that sitting around playing videogames all day."

LARP means "LIVE ACTION ROLEPLAY".
However, in an all time low interview found on buzznet:
alltimelow.buzznet.com (LARPing video)
Jack and Alex turn it into a bad word xD
I think it should be a new slang word for jizz xP